1. Field of Invention
The invention relates to an apparatus and a method for the further processing of semi-finished sacks and a gluing station for semi-finished sacks.
2. Description of the Prior Art
Apparatuses for the further processing of semi-finished sacks are used in the production of a wide variety of sacks. The term “method for the further processing of semi-finished sacks” is understood to mean that at least one portion of the process steps occurring between the presence of the sack material and the formation of the finished sack is part of the method.
Sacks produced by means of the overall method include, for example, the so-called valve sacks, into which valve patches are usually inserted during the production of the sack bottoms. The bottoms themselves are frequently in the form of cross-bottoms such as those described, for example, in DE 090 145 48 U1 and DE 3020043 A1. In order to impart a property of permanent coherence to the bottoms and the valve patches inserted therein, parts of the sack bottoms are stuck to each other and/or to the valve patches with the help of glue.
For this purpose, either the regions of the bottom folds or the valve patches assigned thereto to be glued, that is, all the regions that are to be stuck together, are provided with a trace of glue and then stuck to each other by merging and folding them together.
The application of a trace of glue in the proper format is usually carried out in that a format part attached to a rotating roller is brought into contact with a gluing roller or other glue-storing or glue-transferring components during a rotation of the roller and, in doing so, provided with glue. In the further course of the roller rotation, the format plate transfers the glue stored thereon to regions of the subsequent sack bottoms or valve patches that are to be glued. For this purpose, the format part is provided with characteristic ridges that are adapted to a defined sack format. The format parts are replaced for the production of sacks having other formats on the bottoming apparatus. This type of production of traces of glue over the entire surface of semi-finished sacks has proved useful since it enables, inter alia, large amounts of starch-based adhesive that is difficult to handle to be applied in a clean manner and in the proper format.
The term, “application of a trace of glue in the proper format” is understood to mean a form of application that is adapted to suit the type and format of the sack. In this form of application, glue is usually applied over the entire surface of semi-finished sacks, special significance often being accorded to the edges of the format for the durability and the impermeability of the sacks.
However, the associated disadvantage is that this method of glue application makes it necessary to provide a plurality of glue-transfer components, for instance the forming rollers and the format parts for these apparatuses and also again clean the same after use.
Therefore bottoming apparatuses have been disclosed more recently that dispense with such types of format parts. Thus EP 1 648 688 B1 discloses a bottoming apparatus comprising a gluing station, in which a plurality of application heads extrude glue onto semi-finished sacks. For this purpose, a plurality of glue valves is attached to each of these application heads. One or more glue-outlet openings, from which glue is discharged onto the sack components, are assigned to these glue valves.
The application of a trace of glue in the proper format is now carried out in that a control unit selectively activates these glue valves. In this way, a wide variety of glue profiles can be realized and it is no longer necessary to provide a large number of format parts.
DE 103 09 893 A1 also discloses a similar teaching. It can be learned from both documents that glue is applied to semi-finished sacks in a bottoming apparatus comprising a gluing station that has a glue-application head. It can further be concluded that the semi-finished sacks are guided past the application head by means of at least one guide element in such a way that glue can be applied to them.
This is also the case in the apparatuses disclosed in WO 2004/048003 A1 and GB 2 331 150 A.
However, the present invention has shown that particularly semi-finished sacks having more complicated shapes—such as tubular pieces comprising open bottom squares and in this case particularly tubular pieces comprising open bottom squares and valve patches inserted therein—also tend in these apparatuses to be subjected to a partial gluing process or even suffer damages during the process of glue application in the nozzle clearance.